Device and method for acoustic diagnosis and measurement by pulse electromagnetic force

ABSTRACT

The invention provides an acoustic diagnosis/measurement apparatus/method using a pulse of electromagnetic force, capable of non-destructively and precisely diagnosing or measuring corrosion, adhesion, the cover depth, and/or the diameter of a reinforcing iron rod in a structure made of reinforced concrete. A coil  12  is attached to a surface of a structure  11  including a conductor  11   a  and a non-conductive material  11   b  covering the conductor  11   a . A current pulse is applied to the coil  12  thereby generating a magnetic field pulse. The magnetic field pulse causes an eddy current to be induced in the conductor  11   a . The conductor  11   a  is oscillated by interaction between the eddy current and the magnetic field pulse. As a result, an acoustic signal is generated by the conductor  11   a  and the acoustic signal is converted into an eclectic signal by an acoustic transducer  14  disposed to the surface of the structure  11 . The resultant electric signal is measured by a measurement unit  15  to diagnose/measure the location of the conductor  11   a  or the state of the structure  11.

TECHNICAL FIELD

The present invention relates to an acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force fordiagnosing/measuring a structure including a conductor and anon-conductive material covering the conductor, and a method ofdiagnosing/measuring such a structure, in particular, in terms ofcorrosion or adhesion of a reinforcing iron rod in reinforced concrete,the location of the reinforcing iron rod, the diameter of thereinforcing iron rod, presence/absence of a fracture in the reinforcingiron rod, or the location of the fracture, or in terms of the locationof a water pipe buried in the ground, or in terms of whether a conductoris securely bound by a binding member.

BACKGROUND ART

In a structure made of reinforced concrete, such as a tunnel, a bridge,a building, a retaining wall, a dam, or a civil construction, in orderto evaluate the strength or life or to determine construction procedure,it is needed to detect locations of reinforcing iron rods, diameters ofreinforcing iron rods, the degree of corrosion of reinforcing iron rods,and/or adhesion strength of reinforcing iron rods, for the purpose of,for example, evaluation of strength or life of the structure ordetermination of procedure of construction. Various techniques for theabove purpose are known. They include radiography for taking an X-rayimage of a structure placed between an X-ray generator and a film,ultrasonic diagnosis in which an ultrasonic wave is generated by anultrasonic generator placed on the surface of concrete anddiagnosis/measurement is performed on the basis of detection of areflected ultrasonic wave, a percussion method in whichdiagnosis/measurement is performed on the basis of an echo detectedafter tapping a surface of a structure with a hammer or the like, aninfrared imaging method in which a surface of a structure is illuminatedwith an infrared ray, and a microwave method in which a surface of astructure is illuminated with a microwave.

However, the conventional methods of detecting locations of reinforcingiron rods or corrosion of reinforcing iron rods have problems asdescribed below. For example, in radiography, it is needed to put astructure between the X-ray generator and the film, and thus this methodhas various limitations such as those on the shape, the size, and thelocation. This method cannot be substantially used for tunnels, dams, orthe like. Another problem is that control is needed so as to prevent ahuman body from being significantly damaged by an X-ray and thus it isnot easy to employ this method.

In the detection of the locations of reinforcing iron rods using thepercussion method, a high skill is needed. Because detection is based onthe skill, it is difficult to achieve high reliability in detection.When diagnosis of corrosion is performed using this method, corrosioncannot be easily detected unless reinforcing iron rods are sosignificantly corroded that a void is created. In this method, detectionof corrosion is based on the skill and thus the reliability of detectionis low. For this reason, it is needed to partially expose a reinforcingiron rod and visually observe an exposed part to confirm.

In the ultrasonic diagnosis method, an ultrasonic wave is applied to thesurface of reinforced concrete, and the location of a reinforcing ironrod is determined from an ultrasonic wave reflected from the reinforcingiron rod. However, the concrete includes gravel and a large number ofnon-continuous parts created by bubbles or the like, which cause theultrasonic wave to be attenuated or scattered and thus make it difficultto perform analysis.

In the infrared imaging method and also in the microwave method, becausethe infrared ray or the microwave is greatly attenuated by concrete,measurement is possible only in a region near the surface of astructure.

As a for a method of diagnosing corrosion, it is known to detect anacoustic wave generated by elastic energy released when a structure isdeformed or cracked and analyze the detected acoustic wave to determinethe degree of corrosion of the structure. This method is known as anacoustic diagnosis method. More specifically, an acoustic emission (AE)sensor is attached to a structure and the output of the AE sensor ismonitored over a long period of time to detect an acoustic emissionwhich occurs accidentally and suddenly due to stress corrosion cracking.However, it is needed to continuously perform measurement over a longperiod and it is also needed to apply an unnecessarily large load. Thus,this technique is not suitable for detection of corrosion of astructure.

As described above, no conventional method is known which allowshigh-reliability non-destructive detection of the degree of corrosion ofreinforcing iron rods in reinforced concrete, adhesion strength betweenconcrete and reinforcing iron rods, or the location or the diameter of areinforcing iron rod in concrete. The lack of effective methods causesan error to occur in prediction of strength or life, and thus can causean unpredictable disaster to occur.

In structures including a prestressed conductor and a non-conductivematerial covering the conductor, that is, structures made ofprestressed-concrete, such as bridges, electric poles, and railroadties, reinforcing iron rods prestressed so as to enhance theirelasticity are embedded in concrete. When such a structure is used for along period, there is a possibility that a reinforcing iron rodfractures. However, no conventional technique is known which allows sucha fracture to be detected in a non-destructive fashion. Therefore,periodical replacement at scheduled intervals is needed, or otherwise anunpredictable disaster can occur.

In a civil engineering work or a construction work in which it isrequired to drive stakes into ground, it is necessary to know thelocations of existing water pipes or gas pipes buried in the ground. Inthis case, water pipes and gas pipes are conductors embedded in anon-conductive material. Conventionally, a metal detector or sonar isused to determine the buried location. However, such an apparatus iscomplicated and special technical knowledge is needed to handle it.There is no technique which can be easily used to detect a preciselocation under ground. Thus, in many cases, a troublesome job, such asdigging up the ground, is needed to make confirmation.

In the case of a structure including a plurality of conductors boundwith each other via a binding member, such as a bridge constructed as aroad by joining iron plates using bolts and nuts, for the purpose ofsafety, it is necessary to periodically examine whether bolts and nutsare maintained in a securely fastened state. However, in structureshaving a large size such as bridges, large bolts and nuts are used andthey are fastened by very large torque. Therefore, it is impossible tomanually diagnose using a torque wrench or the like, and diagnosis isperformed using a dedicated machine having a large size. Another problemin such diagnosis is that it is necessary to close the bridge during thediagnosis.

In view of the above, a first object of the present invention is toprovide an apparatus for diagnosing or measuring, non-destructively andprecisely, a structure including a conductor and a non-conductivematerial covering the conductor in terms of the degree of corrosion, theadhesive strength, the cover depth, and the diameter of the conductor. Aspecific example is an apparatus for non-destructively diagnosing ormeasuring the degree of corrosion of reinforcing iron rods in reinforcedconcrete, the strength of adhesion between reinforcing iron rods andconcrete, and/or the cover depth or the diameter of reinforcing ironrods in concrete.

A second object of the present invention is to provide an apparatus fornon-destructively and precisely measuring the location of a concoctor ina structure including the conductor and a non-conductive materialcovering the conductor. A specific example is an apparatus fornon-destructively and precisely measuring the location of reinforcingiron rods in reinforced concrete.

A third object of the present invention is to provide an apparatus fordiagnosing or measuring, in detail, the degree of corrosion, theadhesion strength, and/or the location of a conductor in a structureincluding the conductor and a non-conductive material covering theconductor, on the basis of a distribution of small vibrations over theentire surface and a propagation mode of vibrations. A specific exampleis an apparatus for non-destructively diagnosing or measuring the degreeof corrosion of reinforcing iron rods in reinforced concrete, thestrength of adhesion between reinforcing iron rods and concrete, and/orthe location of reinforcing iron rods in concrete.

A fourth object of the present invention is to provide a method ofnon-destructively and precisely diagnosing or measuring the degree ofcorrosion and/or the adhesion strength of a conductor in a structureincluding the conductor and a non-conductive material covering theconductor. A specific example is a method of non-destructivelydiagnosing or measuring the degree of corrosion of reinforcing iron rodsin reinforced concrete and/or the strength of adhesion betweenreinforcing iron rods and concrete.

A firth object of the present invention is to provide a method ofnon-destructively and precisely measuring the location of a conductor ina structure including the conductor and a non-conductive materialcovering the conductor. A specific example is a method ofnon-destructively measuring the location of reinforcing iron rods inreinforced concrete.

A sixth object of the present invention is to provide a method ofnon-destructively and precisely measuring the location of a conductor ina structure including the conductor and a non-conductive materialcovering the conductor. A specific example is a method ofnon-destructively diagnosing or measuring, in detail, the degree ofcorrosion of reinforcing iron rods in reinforced concrete, the strengthof adhesion between reinforcing iron rods and concrete, and/or thelocation of reinforcing iron rods in concrete, on the basis of adistribution of small vibrations over the entire surface and apropagation mode of vibrations.

A seventh object of the present invention is to provide a method ofmeasuring the diameter or the cover depth of a conductor in a structureincluding the conductor and a non-conductive material covering theconductor. A specific example is a method of measuring the diameter orthe cover depth of reinforcing iron rods in reinforced concrete.

An eighth object of the present invention is to provide a method ofdiagnosing or measuring whether conductors bound with each other via abinding member are in a state in which the conductors are securely boundby the binding member. A specific example is a method of diagnosing ormeasuring whether iron plates bound with each other via a bolt and a nutare in a state in which the iron plates are securely bound by the boltand the nut.

A ninth object of the present invention is to provide a method ofnon-destructively and precisely diagnosing or measuring the location ofa conductor embedded in a non-conductive material. A specific example isa method of diagnosing or measuring the location of a water pipe or agas pipe buried under the ground.

A tenth object of the present invention is to provide a method ofnon-destructively and precisely diagnosing or measuring a structureincluding a conductor and a non-conductive material covering theconductor as to whether the conductor has a fracture. A specific exampleis a method of determining whether a bridge, an electric pole, or arailroad tie, which are made of prestressed concrete, has a fractureand/or measuring the location of such a fracture.

DISCLOSURE OF THE INVENTION

To achieve the above objects, the present invention provides an acousticdiagnosis/measurement apparatus using a pulse of electromagnetic force,comprising a coil attached to a surface of a structure including aconductor and a non-conductive material covering the conductor; a powersupply unit for supplying a current pulse to the coil; an acoustictransducer attached to the surface of the structure or to a part of theconductor, the part being separated from the non-conductive material;and a measurement unit for measuring an output waveform of the acoustictransducer, whereby corrosion of the conductor, adhesion strength of theconductor, the cover depth of the conductor, and/or the diameter of theconductor are diagnosed or measured.

In this apparatus, when the structure subjected to the measurement is,for example, reinforced concrete, an acoustic wave is generated from anacoustic wave source at the location of the reinforcing iron roddirectly excited by the magnetic field pulse and the acoustic wavepropagates through the structure to the surface thereof. The acousticwave propagating to the surface of the structure varies depending on thedegree of corrosion and/or adhesion of the reinforcing iron rod.Therefore, by analyzing the acoustic waveform, it is possible todiagnose or measure the degree of corrosion and the adhesion strength.The amplitude of the acoustic waveform also varies depending on thediameter of the reinforcing iron rod and the cover depth of thereinforcing iron rod. If the depth of the reinforcing iron rod is known,the diameter of the reinforcing iron rod can be determined. Conversely,if the diameter of the reinforcing iron rod is known, the cover depthcan be determined.

In this technique, because the reinforcing iron rod is directly excitedby the magnetic field pulse, a very large acoustic waveform can beobtained compared with that obtained in the conventional technique inwhich an ultrasonic wave generated by an ultrasonic source is reflectedfrom the reinforcing iron rod. Furthermore, in this technique accordingto the present invention, unlike the conventional percussion method, thedegree of corrosion, the strength of adhesion, the cover depth, and/orthe diameter of the reinforcing iron rod can be diagnosed or measurednon-destructively in a highly reliable fashion.

The present invention also provides an acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force, comprising a coilattached to a surface of a structure including a conductor and anon-conductive material covering the conductor; a power supply unit forsupplying a current pulse to the coil; a plurality of acoustictransducers attached at different locations on the surface of thestructure; and a measurement unit for measuring acoustic propagationdelays from outputs of the acoustic transducers, whereby the location ofthe conductor is measured.

In this apparatus, an acoustic wave is generated from an acoustic wavesource at the location of the reinforcing iron rod directly excited bythe magnetic field pulse and the acoustic wave propagates through thestructure to the surface thereof. On the basis of propagation delaytimes of the acoustic wave measured at different locations, the locationof the reinforcing iron rod can be precisely determinednon-destructively.

The present invention provides an acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force, comprising a coilattached to a surface of a structure including a conductor and anon-conductive material covering the conductor; a power supply unit forsupplying a current pulse to the coil; and a displacement detector foroptically measuring displacement of the surface of the structure therebymeasuring a vibration of the surface of the structure; whereby thelocation of the conductor, corrosion of the conductor, and/or adhesionstrength of the conductor are diagnosed or measured.

In this apparatus, an acoustic wave is generated from an acoustic wavesource at the location of the reinforcing iron rod directly excited bythe magnetic field pulse and the acoustic wave propagates through thestructure to the surface thereof. By employing a laser interferometer asthe displacement detector, it is possible to detect the distribution ofsmall vibrations over the entire surface and it is also possible todetect the propagation mode of vibrations, and thus it is possible toobtain further detailed information in a non-destructive fashion.

Preferably, the acoustic transducer is an element for converting anacoustic signal into an electric signal, selected from a groupconsisting of an acoustic emission sensor, an acceleration sensor, and amicrophone.

The displacement detector may be a laser interferometer for illuminatinga surface of the structure with a coherent laser beam and detecting aphase difference as an interference pattern of a reflected laser beam,the phase difference varying depending on a vibration of a surface ofthe structure.

The coil may be a single coil or may include a plurality of subcoils. Inthe case in which a plurality of subcoils are used, the plurality ofsubcoils are disposed coaxially such that adjacent coils are in closecontact with each other. The power supply unit may include chargestorage capacitors connected in series to the respective subcoils and apower source connected, via a common switch and in parallel, to eachseries connection of one subcoil and one capacitor, whereby a currentpulse is applied to subcoils by turning on the common switch therebygenerating a magnetic field pulse.

When the coil is formed using a plurality of subcoils, the inductance ofeach of subcoils forming the coil is smaller than is in the case inwhich the coils is formed of a single coil, and the capacitor of eachcharge storage capacitor can be reduced. This makes it possible toreduce the time constant of a current pulse which flows through eachsubcoil in response to turning on the common switch. The magnetic fieldpulses generated by the subcoils are superimposed, and thus it ispossible to generate an overall magnetic field pulse having a largecrest value and a small pulse width. The capability of generating amagnetic field pulse with a large crest value and a small pulse widthmakes it possible to strongly excite a reinforcing iron rod, whichallows diagnosis/measurement to be performed non-destructively in a highreliable fashion.

It is desirable to add a magnet for generating a static magnetic fieldto the coil.

This makes it possible to further strongly excite the reinforcing ironrod and thus it makes possible to perform diagnosis/measurement of areinforcing iron rod located at deeper depth with respect to the surfaceof the structure.

The measurement unit for measuring the output waveform may measure theoutput waveform in the time domain, display the measured outputwaveform, extract a feature associated with corrosion and/or adhesionfrom the waveform in the time domain, and display the extracted feature,or may calculate a waveform in the frequency domain, that is, afrequency spectrum, by performing a Fourier transform on the originaloutput waveform, display the calculated waveform in the frequencydomain, extract a feature associated with corrosion and/or adhesion fromthe waveform in the frequency domain, and display information associatedwith the corrosion and/or adhesion.

This measurement unit is capable of instantly performingdiagnosis/measurement of corrosion and/or corrosion from the waveform inthe time domain or frequency domain.

The feature extracted from the waveform in the time domain may be apattern, a shape factor, or a crest factor of the waveform in the timedomain, and the displaying of information associated with the corrosionand/or adhesion may include comparing the form factor or the crestfactor with a predetermined threshold value and displaying whether ornot there is a problem in terms of the corrosion and/or the adhesion.

The shape factor and the crest factor vary sensitively depending oncorrosion and/or adhesion, and thus it is possible to easily detectcorrosion and/or adhesion from the shape factor and the crest factor.The measured shape factor or crest factor is compared with apredetermined threshold value, and information whether there is aproblem in terms of corrosion/adhesion is displayed. Thus, any user cancorrectly perform diagnosis/measurement without having to have a highskill.

The feature extracted from the waveform in the time domain may be asimilarity factor extracted from the shape of the envelope curve of thewaveform in the time domain, and the displaying of informationassociated with the corrosion and/or adhesion may include comparing thesimilarity factor with a predetermined threshold value and displayingwhether or not there is a problem in terms of the corrosion and/or theadhesion.

Aging effects are reflected in the similarity factor, and thushigh-reliability diagnosis/measurement can be performed on the base ofthe similarity factor. The measured similarity factor is compared with apredetermined threshold value, and information whether there is aproblem in terms of corrosion/adhesion is displayed. Thus, any user cancorrectly perform diagnosis/measurement without having to have a highskill.

The feature extracted from the waveform in the time domain may be anormalized waveform obtained by dividing each value of the waveform inthe time domain by the effective value of the waveform in the timedomain or a waveform obtained by exponentiation of the normalizedwaveform.

If the waveform in the time domain is normalized by dividing each valueof the waveform in the time domain by the effective value of thewaveform in the time domain, the feature of the original waveformbecomes clearer. The feature of the original waveform becomes furtherclearer by exponentiation. Thus, it becomes possible to performhigh-sensitive diagnosis/measurement.

The similarity factor may be extracted from the envelope curve of thenormalized waveform and compared with a predetermined threshold value.Depending on the comparison result, information indicating whether ornot there is a problem in terms of the corrosion and/or the adhesion maybe displayed.

Because the similarity factor is determined from the normalizedwaveform, it becomes possible for any user to easily perform correctdiagnosis/measurement in a further sensitive fashion.

The feature extracted from the waveform in the frequency domain may be awaveform pattern in the frequency domain, and the displaying ofinformation associated with the corrosion and/or adhesion may includecomparing the waveform pattern with a predetermined pattern, anddisplaying whether or not there is a problem in terms of the corrosionand/or the adhesion.

In the vibration of a reinforcing iron rod excited by a pulse ofelectromagnetic force, the degree of freedom of vibration variesdepending on corrosion/adhesion of the reinforcing iron rod, and thusthe degree of corrosion/adhesion is very sensitively reflected in thefrequency spectrum. Because information is displayed which indicateswhether or not there is a problem in terms of corrosion/adhesiondetermined based on the comparison of the frequency spectrum with apredetermined reference frequency pattern, any user can easily performcorrect diagnosis/measurement without having to have a high skill.

The feature extracted from the waveform in the frequency domain may be anormalized waveform obtained by dividing each value of the waveform inthe frequency domain by the effective value of the waveform in the timedomain or a waveform obtained by the exponentiation of the normalizedwaveform, and the displaying of information associated with thecorrosion and/or adhesion may include extracting the similarity factorfrom the envelope curve of the normalized waveform, comparing thesimilarity factor with a predetermined threshold value, and displayingwhether or not there is a problem in terms of the corrosion and/or theadhesion.

The waveform in the frequency domain is very sensitive to the degree ofcorrosion and/or adhesion strength. If this waveform in the frequencydomain is normalized by dividing each value of the waveform in thefrequency domain by the effective value, the feature of the originalwaveform is emphasized in the resultant normalized waveform. Thus,highly sensitive diagnosis/measure of corrosion/adhesion is possible.Furthermore, if the similarity factor is determined from the normalizedwaveform, high-sensitive and high-reliability diagnosis/measurement ispossible. The measured similarity factor is compared with apredetermined threshold value, and information whether there is aproblem in terms of corrosion/adhesion is displayed. Thus, any user cancorrectly perform diagnosis/measurement without having to have a highskill.

The displacement detector may be a laser interferometer for illuminatinga surface of the structure with a coherent laser beam and detecting aphase difference as an interference pattern of a reflected laser beam,the phase difference varying depending on a vibration of a surface ofthe structure.

The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of attaching a coil to a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into an electric signal by usingan acoustic transducer attached to the surface of the structure orattached to a part of the conductor, the part of the conductor beingseparated from the non-conductive material; and measuring the waveformof the electric signal to perform diagnosis and/or measurement in termsof corrosion and/or adhesion of the conductor.

In this method, when the structure subjected to the measurement is, forexample, reinforced concrete, an acoustic wave is generated from anacoustic wave source at the location of the reinforcing iron roddirectly excited by the magnetic field pulse and the acoustic wavepropagates through the structure to the surface thereof. The acousticwave propagating to the surface of the structure varies depending on thedegree of corrosion and/or adhesion of the reinforcing iron rod.Therefore, by analyzing the acoustic waveform, it is possible todiagnosing or measuring the degree of corrosion and the adhesionstrength.

In this technique, because the reinforcing iron rod is directlyoscillated by the magnetic field pulse, a very large acoustic waveformcan be obtained compared with that obtained in the conventionaltechnique in which an ultrasonic wave generated by an ultrasonic sourceis reflected from the reinforcing iron rod. Thus, the degree ofcorrosion, the strength of adhesion, the cover depth, and/or thediameter of the reinforcing iron rod can be diagnosed or measurednon-destructively.

The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of attaching a coil to a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into electric signals by using aplurality of acoustic transducers attached at different locations on thesurface of the structure; and measuring propagation delay times of theacoustic wave corresponding to the respective electric signals; andmeasuring the location of the conductor on the basis of the propagationdelay times.

In this method, an acoustic wave is generated from an acoustic wavesource at the location of the reinforcing iron rod directly excited bythe magnetic field pulse and the acoustic wave propagates through thestructure to the surface thereof. On the basis of propagation delaytimes of the acoustic wave measured at different locations, the locationof the reinforcing iron rod can be precisely determinednon-destructively.

The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of attaching a coil to a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; detectingan optical displacement corresponding to a surface vibration of thestructure generated by the acoustic wave thereby diagnosing the locationof the conductor and the state of the structure.

In this method, an acoustic wave is generated from an acoustic wavesource at the location of the reinforcing iron rod directly excited bythe magnetic field pulse and the acoustic wave propagates through thestructure to the surface thereof. By employing a laser interferometer asthe displacement detector, it is possible to detect the distribution ofsmall vibrations over the entire surface and it is also possible todetect the propagation mode of vibrations, and thus it is possible toperform further detailed diagnosis in a non-destructive fashion.

The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of disposing a coil on a surface of a non-conductive materialcovering a conductor; applying a current pulse to the coil therebygenerating a magnetic field pulse; inducing an eddy current in theconductor by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; converting an acoustic signal ofthe acoustic wave into an electric signal by using an acoustictransducer attached to the surface of the structure; and measuring thewaveform of the electric signal to measure the diameter of the conductoror measure the cover depth of the conductor.

In this method, the amplitude of the acoustic waveform varies dependingon the diameter of the reinforcing iron rod and the cover depth of thereinforcing iron rod. If the depth of the reinforcing iron rod is known,the diameter of the reinforcing iron rod can be determined. Conversely,if the diameter of the reinforcing iron rod is known, the cover depthcan be determined.

The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of disposing a coil at a location exactly above a connectingpart of a plurality of conductors bound with each other via a bindingmember; applying a current pulse to the coil thereby generating amagnetic field pulse; inducing an eddy current in a conductor facing thecoil by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; converting an acoustic signal ofthe acoustic wave into an electric signal by using an acoustictransducer attached to the conductor facing the coil and by using anacoustic transducer attached to another conductor bound with the formerconductor; and comparing the waveform of the electric signal output bythe acoustic transducer attached to the conductor facing the coil withthe waveform of the electric signal output by the acoustic transducerattached to the other conductor, thereby performing diagnosis and/ormeasurement as to whether the binding member is in a securely fastenedstate.

In this method, the magnitude of a vibration propagating into theconductor from the other conductor facing the coil varies depending onthe fastening degree. Thus, the fastening degree can be diagnosed ormeasured. This method is useful in particular when a set of a bolt and anut is used as the binding member.

The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of disposing a coil on a surface of a non-conductive materialcovering a conductor; applying a current pulse to the coil therebygenerating a magnetic field pulse; inducing an eddy current in theconductor by the magnetic field pulse; oscillating the conductor byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave; converting an acoustic signal ofthe acoustic wave into an electric signal by using an acoustictransducer attached to a part of the conductor, the part of theconductor being separated from the non-conductive material; changing thelocation of the coil disposed on the surface of the non-conductivematerial; and measuring a change in the electric signal caused by thechange in the location of the coil there by measuring the location ofthe conductor.

In this method, the conductor is oscillated most strongly when the coilcomes to a location closest to the conductor. Thus, the location of theconductor can be diagnosed or measured. This method is useful inparticular when the conductor is an underground water pipe or gas pipe.

The present invention also provides a method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of attaching a coil to a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into an electric signal by usingan acoustic transducer attached to a part of the conductor, the part ofthe conductor being separated from the non-conductive material; anddiagnosing whether the conductor has a fracture, on the basis of thestrength of the electric signal and, if necessary, diagnosing thelocation of the fracture of the conductor by changing the location ofthe coil disposed on the surface of the structure and measuring a changein the electric signal caused by the change in the location of the coil.

In this method, an acoustic signal propagating through a reinforcingiron rod is attenuated by a fracture, and thus it is possible to detectwhether or not there is a fracture. Furthermore, if a change inattenuation is measured while changing the location of the coil disposedon the surface of a structure, it is possible to detect the location ofthe fracture. This method is useful in particular when the structure ismade of prestressed concrete, such as a bridge, an electric pole, or arailroad tie made of prestressed concrete.

Thus, according to the present invention, it is possible tonon-destructively and precisely diagnose/measure not only the locationof an reinforcing iron rod in concrete but also corrosion, adhesionstrength, and/or rust of the reinforcing iron rod and further aseparation or a crack of concrete in diagnosis/measurement of astructure made of reinforced concrete, such as a tunnel, a bridge, abuilding, a retaining wall, a dam, or a civil construction. This makesit possible to prevent a structure made of reinforced concrete frombreaking down or prevent a piece of concrete from separating from themain part. Thus it becomes possible to precisely predict the remaininglife of a structure made of reinforced concrete and performmaintenance/management of the structure made of reinforced concrete in ahighly reliable fashion.

The cover depth and/or the diameter of a reinforcing iron rod can alsobe measured.

It is also possible to easily determine whether a binding member such asa set of a bolt and a nut is securely fastened.

It is also possible to easily determine the location of a water pipe ora gas pipe buried in the ground.

It is also possible to diagnose whether a reinforcing iron rod has afracture.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent from the followingdetailed description of the preferred embodiments with reference to theaccompanying drawings. Note that the embodiments described withreference to the accompanying drawing are presented for the purpose ofillustration and ease of understanding of the invention and are notintended to limit the invention.

FIGS. 1(a) and 1(b) are conceptual diagrams showing the embodiment ofthe acoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force according to claim 1 of the present invention andthe method therefor, FIG. 1(a) shows a manner in which an acoustictransducer is attached to a surface of concrete, FIG. 1(b) shows amanner in which the acoustic transducer is attached to an exposed partof an iron rod.

FIGS. 2(a) and 2(b) are diagrams showing the shape of a test sample ofreinforced concrete used herein in the first example and also showing ameasurement system, wherein FIG. 2(a) is a plan view and FIG. 2(b) is aside view thereof.

FIGS. 3(a) and 3(b) are diagrams showing measured acoustic waveforms,wherein an acoustic waveform observed for the normal block is shown inFIG. 3(a) and an acoustic waveform observed for the cracked block isshown in FIG. 3(b).

FIG. 4 is a schematic diagram showing an acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force according to thepresent invention.

FIG. 5(a) to 5(c) show the surface shape of reinforced concrete used inan embodiment and a method of producing the reinforced concrete, whereinFIG. 5(a) shows the surface shape of the reinforced concrete, FIG. 5(b)shows an outer frame used to produce the reinforced concrete, and FIG.5(c) shows the external appearance of produced reinforced concrete.

FIG. 6 is a diagram showing propagation delay times in the reinforcedconcrete, measured at different distances from the acoustic wave source.

FIG. 7 is a graph showing a manner in which the velocity of an acousticwave propagating through concrete is determined from propagation delaytimes measured at various distances from an acoustic wave source.

FIG. 8(a) shows a coil and a power supply unit according to aconventional technique, and FIG. 8(b) shows a coil and a power supplyunit according to the present invention.

FIGS. 9(a) and 9(b) show an example of the waveform of a current pulseapplied to a coil from a power source and an example of a measuredacoustic signal generated thereby, wherein the example shown in FIG.9(a) is according to a conventional technique, and the example shown inFIG. 9(b) is according to the present invention.

FIGS. 10(a), 10(b), and 10(c) are diagrams showing waveforms in the timedomain output by the acoustic transducers attached to the respectivetest blocks (A), (B), and (C) and measured by the measurement unit.

FIGS. 11(a), 11(b), and 11(c) are diagrams showing waveforms in the timedomain output by the acoustic transducers directly attached toreinforcing iron rods of the respective test blocks (A), (B), and (C)and measured by the measurement unit.

FIG. 12 is a table showing the shape factors SF and the crest factors CFfor the respective test blocks (A), (B), and (C).

FIG. 13(a) shows the envelope curves determined for the respective testblocks (A), (B), and (C), and FIG. 13(b) shows the correspondinglogarithmic inverse envelope curves.

FIGS. 14(a), 14(b), and 14(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (A).

FIGS. 15(a) and 14(b) respectively show the cube and the quartic of thenormalized waveform of the test block (A).

FIGS. 16(a), 16(b), and 16(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (B).

FIGS. 17(a) and 17(b) respectively show the cube and the quartic of thenormalized waveform of the test block (B).

FIGS. 18(a), 18(b), and 18(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (C).

FIGS. 19(a) and 19(b) respectively show the cube and the quartic of thenormalized waveform of the test block (C).

FIGS. 20(a), 20(b), and 20(c) respectively show frequency-domainwaveforms of the test blocks (A), (B), and (C), determined from thetime-domain waveforms determined in the third example for the testblocks (A), (B), and (C).

FIGS. 21(a), 21(b), and 21(c) respectively show frequency-domainwaveforms of the test blocks (A), (B), and (C), determined from thetime-domain waveforms determined in the fourth example for the testblocks (A), (B), and (C).

FIG. 22(a) is a diagram showing a method of measuring the diameter orthe cover depth of a reinforcing iron rod according to the presentinvention, and FIG. 22(b) is a graph showing a measurement result.

FIGS. 23(a) and 23(b) are diagrams showing a method of diagnosing ormeasuring the secureness of a binding member, according to the presentinvention, wherein FIG. 23(a) is a side view of a conductor 21 and aconductor 22 bound together via a bolt 22 and a nut 23, and FIG. 23(b)is a plan view thereof.

FIGS. 24(a) to 24(d) are diagrams showing a measurement result obtainedwhen the bolt and the nut are securely fastened, wherein FIGS. 24(a) and24(b) show output waveforms of an acoustic transducer 14R attached tothe conductor 21 located closer to a coil, and FIGS. 24(c) and 24(d)show output waveforms of an acoustic transducer 14L attached to theconductor 22 bound with the conductor 21 by the bolt and the nut.

FIGS. 25(a) to 25(d) are diagrams showing a measurement result obtainedwhen the bolt and the nut are in a loosely coupled state, wherein FIGS.25(a) and 25(b) show output waveforms of the acoustic transducer 14Rattached to the conductor 21 located closer to a coil, and FIGS. 25(c)and 25(d) show output waveforms of the acoustic transducer 14L attachedto the conductor 22 bound with the conductor 21 by the bolt and the nut.

FIGS. 26(a) and 26(b) are diagrams showing a method of measuring thelocation of a conductor embedded in a non-conductive material, whereinFIG. 26(a) is a side view showing a manner in which an acoustictransducer 14 is attached to an exposed part 33 of a water pipe 32buried in the ground 31 which is non-conductive, and a coil 12 isdisposed on the surface 34 of ground 31, and FIG. 26(b) is a plan viewthereof.

FIGS. 27(a) to 27(c) are graphs showing results of measurement of thelocation of a water pipe buried in the ground, wherein FIG. 27(a) showsthe waveform of an acoustic signal detected by the coil disposed exactlyabove the water pipe, FIG. 27(b) shows a waveform detected by the coildisposed on the ground at a location 60 mm apart from the locationexactly above the water pipe, FIG. 27(c) shows a waveform detected bythe coil disposed on the ground at a location 180 mm apart from thelocation exactly above the water pipe.

FIG. 28 is a diagram showing a method of diagnosing whether a conductorembedded in a non-conductive material has a fracture and a method ofmeasuring the location of the fracture.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are described in detail below withreference to drawings.

First, an embodiment of an acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force according to the presentinvention and a method therefor are described.

Herein, by way of example, the structure including a conductor and anon-conductive material covering the conductor subjected todiagnosis/measurement is assumed to be a structure made of concretereinforced with iron rods.

The apparatus of the present embodiment is capable of makingdiagnosis/measurement in terms of corrosion, adhesion, cover depth, anddiameters of iron rods.

FIGS. 1(a) and 1(b) are conceptual diagrams showing the embodiment ofthe acoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force according to the present invention and the methodtherefor, wherein FIG. 1(a) shows a manner in which an acoustictransducer is attached to a surface of concrete, and FIG. 1(b) shows amanner in which the acoustic transducer is attached to an exposed partof an iron rod.

In FIG. 1(a), the acoustic diagnosis/measurement apparatus using a pulseof electromagnetic force 10 includes a coil of an electric wire 12attached to a surface of a reinforced concrete block 11 which is astructure to be examined, a power supply unit 13 for applying a currentpulse to the coil 12, an acoustic transducer 14 attached to the surfaceof the reinforced concrete block 11, and a measurement unit 15 connectedto the acoustic transducer 14 via a signal cable 17.

The coil 12 includes four coils each formed of 7 turns of a conductivewire with a diameter of, for example, 1.6 mm wound around arectangular-shaped frame with a size of 50 mm×30 mm wherein those fourcoils are disposed coaxially and closely. The coil 12 is attached to thesurface of the reinforced concrete block 11 to be examined. The powersupply unit 13 is designed to apply a current pulse to the coil 12 via apower cable 16. The power supply unit 13 may be constructed in variousmanners depending on the size of the reinforced concrete block 11 andthe location of the reinforcing iron rod 11 a so that a desirabledriving pulse is applied.

As for the acoustic transducer 14, a known acoustic transducer may beemployed to detect a weak vibration and convert the detected vibrationinto an electric signal. The resultant electric signal is supplied tothe measurement unit 15 via the signal cable 17.

As for the measurement unit 15, for example, a commercially availableapparatus known as acoustic analyzer may be employed. The signaldetected by the acoustic transducer 14 is amplified by an amplifier, andunnecessary components of the signal are removed by using a filter orthe like. Acoustic analysis is then performed on the basis of theresultant signal. Another apparatus may also be used as the measurementunit 15. For example, in a case in which it is needed to measure onlythe waveform of the signal detected by the acoustic transducer 14, anoscilloscope or similar equipment may be employed.

In the acoustic diagnosis apparatus using a pulse of electromagneticforce 10 constructed in the above-described manner according to thepresent invention, if a current pulse is applied to the coil 12, amagnetic field pulse is generated toward the inside of the reinforcedconcrete 11, and the magnetic field pulse induces an eddy current in thereinforcing iron rod 11 a which is conductive. A magnetic field isgenerated by the eddy current and it interacts with the magnetic fieldof the magnetic field pulse. As a result, the reinforcing iron rod 11 ais oscillated. Herein, if the conductor 11 a is made of a magneticmaterial, reinforcing iron rod 11 a is further oscillated by a forceassociated with magnetic energy.

If the reinforcing iron rod 11 a is oscillated, an acoustic wave isgenerated from the reinforcing iron rod 11 a. The generated acousticwave propagates to the surface and is detected by the acoustictransducer 14. The detected acoustic signal is converted into anelectrical signal by the acoustic transducer 14 and supplied to themeasurement unit 15 via the signal cable 17. The measurement unit 15analyzes the waveform of the received electric signal to determine thedegree of corrosion of the reinforcing iron rod 11 a or determinewhether the concrete 11 b has a crack. If the reinforcing iron rod 11 ahas corroded, the acoustic wave generated by the reinforcing iron rod 11a is absorbed by a corroded portion, and attenuation of the acousticwave occurs, which results in a reduction in the amplitude of thewaveform observed by the measurement unit 15. Also in a case in whichadhesion between the reinforcing iron rod and the concrete is weak, theamplitude of the waveform detected by the measurement unit 15 becomessmall. A crack in the concrete results in attenuation of the acousticwave, and thus the amplitude of the waveform detected by the measurementunit 15 becomes small. As described above, by comparing the amplitude ofthe acoustic wave, it is possible to detect the degree of damage of thereinforced concrete 11.

As shown in FIG. 1(b), it is also possible to detect corrosion oradhesion of a reinforcing iron rod by attaching the acoustic transducer14 to an exposed portion of the reinforcing iron rod and directlydetecting a vibration of the reinforcing iron rod.

Now, a first example is described.

In this first example, an example of measurement using the acousticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to the present invention is described.

FIGS. 2(a) and 2(b) are diagrams showing the shape of a test sample ofreinforced concrete used herein in the first example and also showing ameasurement system, wherein FIG. 2(a) is a plan view and FIG. 2(b) is aside view thereof.

As shown in FIGS. 2(a) and 2(b), the test sample of reinforced concrete11 includes rectangular-shaped concrete 11 b with a size of 200 mm×150mm×100 mm and a reinforcing iron rod 11 a with a diameter of 13 mmembedded at a cover depth d of 30 mm measured from the upper surface ofthe concrete 11 b and at a distance of 57 mm from the lower surface. Thecoil 12 is disposed on the surface of the reinforced concrete 11 at alocation exactly above the reinforcing iron rod 11 a. The acoustictransducers 14 a and 14 b are disposed on the surface of the reinforcedconcrete 11, at symmetrical locations opposing each other via thereinforcing iron rod 11 a.

In the present example, a test sample of reinforced concrete with nocrack in concrete 11 b (normal test block) and a test sample ofreinforced concrete with a crack extending in concrete 11 b and reachinga reinforcing iron rod 11 a (test block with crack) were prepared andthey were excited under the same conditions. Acoustic waves weredetected by the acoustic transducers 14 a and 14 b and the waveformswere compared.

The coil 12 used herein was formed by winding 25 turns an electric wirewith a diameter of 1.0 mm around a core with a size of 30 mm×70 mm andhad an internal resistance of 0.2 Ω. A current pulse with a crest valueof 1000 A and a width of 1.5 ms was applied to the coil 12 therebyexciting the reinforcing iron rod 11 a.

FIGS. 3(a) and 3(b) are diagrams showing measured acoustic waveforms,wherein an acoustic waveform observed for the normal block is shown inFIG. 3(a) and an acoustic waveform observed for the cracked block isshown in FIG. 3(b).

In FIGS. 3(a) and 3(b), CH1 and CH2 denote output waveforms of theacoustic transducers 14 a and 14 b, respectively, and CH3 denotes thewaveform of the current pulse. The horizontal axis represents a time inunits of 0.5 ms/div and the vertical axis represents the strength of thewaveforms CH1 and CH2, wherein zero points of CH1 and CH2 are shiftedfrom each other.

As can be seen from FIGS. 3(a) and 3(b), the crack significantlyattenuates the acoustic wave generated by the reinforcing iron rod 11 aexcited by the current pulse.

Thus, it is possible to determine whether concrete has a crack.

Now, an embodiment of an acoustic diagnosis/measurement apparatus usinga pulse of electromagnetic force according to the present invention anda corresponding method of acoustic diagnosis/measurement using a pulseof electromagnetic force are described below.

This apparatus is capable of measuring the location of a reinforcingiron rod in reinforced concrete.

FIG. 4 is a conceptual diagram showing an acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force according to thepresent invention and a corresponding method.

As shown in FIG. 4, an acoustic location detector 20 includes a coil ofan electric wire 12 attached to a surface of a reinforced concrete block11, a power supply unit 13 (similar to that shown in FIG. 1, althoughnot shown in FIG. 4) for applying a current pulse to the coil 12, aplurality of acoustic transducers 14 (14 a, 14 b, and 14 c) attached tothe surface of the reinforced concrete block 11, and a measurement unit15 (similar to that shown in FIG. 1 although not shown in FIG. 4)connected to the acoustic transducers 14 via a signal cable 17 (similarto that shown in FIG. 1 although not shown in FIG. 4).

The plurality of acoustic transducers 14 are disposed around the coil12, and the coil 12 is excited by applying a current pulse theretothereby generating an acoustic wave from the reinforcing iron rod 11 a.The acoustic wave is detected and converted into electric signals by therespective acoustic transducers 14, and the resultant electric signalsare supplied to the measurement unit 15. The measurement unit 15determines propagation delay times, that is, times needed for theacoustic wave to propagate from the acoustic wave source to therespective acoustic transducers 14.

The propagation velocity of the acoustic wave in the concrete 11 b canbe regarded to be substantially constant. Therefore, from thepropagation velocity v and the delay times t, it is possible todetermine, the distances r from the acoustic wave source to therespective acoustic transducer 14, that is, the distances from thereinforcing iron rod 11 a to the respective acoustic transducer 14. Fromthose distances, it is possible to determine the location of theacoustic wave source, that is, the location of the reinforcing iron rod11 a.

For example, in a case in which the reinforcing iron rod 11 a has theshape of a rod such as that shown in FIG. 4, if the distances ra, rb,and rc (=v·ta, v·tb, and v·tc) from the acoustic wave source to thereinforcing iron rod 11 a are determined from the propagation delaytimes ta, tb, and tc detected by the acoustic transducers 14 a, 14 b and14 c, and if spheres with radii ra, rb, and rc, respectively, are drawnso that the center of each sphere is located at the correspondinglocation of the acoustic transducer 14, then the location of thereinforcing iron rod 11 a is given by a common point of contact ofspheres.

Although in the above-described example, a plurality of acoustictransducers 14 are disposed on the surface of the concrete 11 and thepropagation delay times at the locations of the acoustic transducers 14are simultaneously measured for a single acoustic signal, thepropagation delay times at various locations may be measured using asingle acoustic transducer 14 in such a manner that the location of theacoustic transducer 14 is changed across the surface of the concrete 11,an acoustic signal is generated at each location and the propagationdelay time is measured.

Now, a second example is described.

In this second example, an example of measurement using the acousticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to the present invention is described.

FIG. 5(a) to 5(c) show the surface shape of reinforced concrete used inan embodiment and a method of producing the reinforced concrete, whereinFIG. 5(a) shows the shape of a surface of the reinforced concrete, FIG.5(b) shows an outer frame used to form the reinforced concrete, and FIG.5(c) shows the external appearance of produced reinforced concrete. Asshown in FIG. 5(b), the reinforced concrete used in this example wasproduced by pouring concrete into the outer frame, in the center ofwhich a reinforcing iron rod 11 a covered, except for its center, withan elastic plastic sheet was disposed, so that only the central portionof the reinforcing iron rod 11 a was brought into contact with theconcrete 11 b and the other portion was not in contact with the concrete11 b. In this structure, a generated acoustic wave propagates into theconcrete from the center of the reinforcing iron rod 11 a, and thus theacoustic wave source can be regarded as a point source.

As shown in FIG. 5(a), the center of the reinforced concrete 11 wastaken as the origin and the horizontal and vertical axes were taken as xand y axes, respectively. The coil was disposed at the origin, and thelocation of the acoustic transducer was represented by coordinates (x,y). The propagation delay time of the acoustic wave detected by theacoustic transducer was measured for various values of coordinates (x,y). The exciting coil, the acoustic transducer, and the current pulseused herein are similar to those used in the first example.

FIG. 6 is a diagram showing propagation delay times in the reinforcedconcrete, measured at different distances from the acoustic wave source.

In FIG. 6, CH1 and CH2 denote acoustic waveforms detected by theacoustic transducer placed at coordinates (−1, 0) and (3, 2),respectively, shown in FIG. 5(a), and CH3 denotes the waveform of thecurrent pulse. The horizontal axis represents the time in units of 0.1ms/div and the vertical axis represent the voltage corresponding to thestrength of the acoustic waveforms denoted by CH1 and CH2, wherein thezero point of the voltage axis for CH1 was shifted from that for CH2.

As can be seen from FIG. 6, the acoustic waveform CH1 detected at aposition near the acoustic wave source appears at substantially the sametime as the current pulse rises. In contrast, the acoustic waveform CH2detected at a position distant from the acoustic wave source appearsafter a rather large delay from the leading edge of the current pulse.

Thus, it is possible to detect the distance from the acoustic powersource by detecting the propagation delay time.

FIG. 7 is a graph showing a manner in which the velocity of an acousticwave propagating through concrete is determined from propagation delaytimes measured at various distances from an acoustic wave source.

In FIG. 7, the distance from the acoustic wave source denotes thedistance between each coordinate point shown in FIG. 6(a) and theacoustic wave source. The propagation delay time was measured in thesame manner as described above with reference to FIG. 7.

As can be seen from FIG. 7, the velocity of the acoustic wavepropagating through concrete can be regarded as constant.

Therefore, the distance to the acoustic wave source can be determinedfrom the propagation delay time described with reference with FIG. 6 andthe velocity of the acoustic wave described with reference with FIG. 7.If the distance to the acoustic wave source is measured at a largenumber of points, the location of the reinforcing iron rod can be givenby a location which satisfies all measured distances.

As described above, the acoustic location detector using a pulse ofelectromagnetic force according to the present invention is capable ofnon-destructively detecting the location of a reinforcing iron rod.

Now, an acoustic diagnosis/measurement apparatus according to thepresent invention is described.

This acoustic diagnosis/measurement apparatus is similar to the acousticdiagnosis/measurement apparatus 10 except that the acoustic transducer14 is replaced by a surface displacement detector and a surfacevibration of a structure 11 to be examined is detected instead of anacoustic wave.

Although any type of detector may be employed as the surfacedisplacement detector as long as it is capable of measuring a smalldisplacement, it is desirable to use a laser interferometer becauseprecise and detailed diagnosis is possible by illuminating the entiresurface of the structure 11 to be diagnosed with coherent laser lightand detecting an interference pattern indicating the phase difference ofa reflected light caused by the surface vibration of the structure 11.

The coil and the power supply unit used in the acousticdiagnosis/measurement apparatus according to the present invention aredescribed below.

FIG. 8(a) shows a coil and a power supply unit according to aconventional technique, and FIG. 8(b) shows a coil and a power supplyunit according to the present invention.

In the conventional technique, as shown in FIG. 8(a), the coil isconstructed in the form of a single piece of coil, and a current pulseis applied to the coil 12 in such a manner that the capacitor C ischarged by an AC voltage V supplied from commercial electric power andthe charge stored in the capacitor C is transferred to the coil 12 byturning on the switch SW which may be a mechanical switch or asemiconductor switch.

On the other hand, in the present invention, as shown in FIG. 8(b) coilsis divided into a plurality of subcoils 12 each having small inductance,and the subcoils 12 are disposed coaxially and closely such thatmagnetic fields generated by the respective coils are superimposed. Acapacitor C is connected in series to each subcoil, and four seriescircuits each consisting of one coil 12 and one capacitor C areconnected in parallel to a common power supply V via a common switch SWwhich may be a mechanical switch or a semiconductor switch.

In this circuit configuration, the coil in each series circuit has smallinductance and the capacitor in each series circuit has smallcapacitance, and thus a current pulse with a small time constant can besupplied when the switch SW is turned on. The magnetic field pulsesgenerated by the respective coils are superimposed and thus a resultantoverall magnetic pulse has a small pulse width and a large crest value.

FIGS. 9(a) and 9(b) show an example of the waveform of a current pulseapplied to a coil from a power source and an example of a measuredacoustic signal generated thereby, wherein the example shown in FIG.9(a) is according to a conventional technique, and the example shown inFIG. 9(b) is according to the present invention. The acoustic wavesignal was measured using the acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force according to the presentinvention. Reinforced concrete including a reinforcing iron rod 13D(deformed reinforcing iron rod with a diameter of 13 mm) with a coverdepth d of 30 mm was used as a test sample. As can be seen from FIG. 9,the coil and the power supply constructed in the above-described manneraccording to the present invention are capable of supplying a currentpulse with a much smaller pulse width and a much larger height than canbe achieved by the conventional technique.

Furthermore, by employing the coil and the power supply according to thepresent invention, a waveform detected by the acoustic emission (AE)sensor, that is, the output waveform of the acoustic transducer becomesmuch greater than can be achieved by the conventional technique.

As described above, by forming the coil and the power supply in theabove-described manner according to the present invention, it becomespossible to generate a magnetic field pulse with a small pulse width anda large crest value, which can strongly excite a reinforcing iron rod.

A measurement unit used in the apparatus in an embodiment of the presentinvention is described below.

The measurement unit according to the present invention samples theoutput waveform of the acoustic transducer, converts the sampled valueinto digital data, stores the resultant digital data into a memory,performs a particular calculation on the digital data via a CPUaccording to a particular signal processing program, and stores theresult into a memory or displays the result on a display. The particularsignal processing program includes a program of displaying a time-domainwaveform of the output waveform, a program of calculating afrequency-domain waveform, that is, frequency spectrum obtained byperforming a Fourier transform on the time-domain waveform of the outputwaveform, and other various signal processing programs which will bedescribed later. The sampling apparatus, the analog-to-digitalconverter, the memory, the CPU, and the display may be those which arecommercially available.

By employing the measurement unit constructed in the above describedmanner, it is possible to measure the waveform in the time domain anddisplay information associated with corrosion and/or adhesion.Furthermore, it is possible to extract a feature associated withcorrosion and/or adhesion from the waveform in the time domain anddisplay the extracted feature. It is also possible to calculate thewaveform in the frequency domain, that is, the Fourier transformspectrum of the output waveform, extract a feature associated withcorrosion and/or adhesion from the waveform in the frequency domain, anddisplay information associated with corrosion and/or adhesion.

Now, a third example is described below.

In this third example, it is demonstrated that a feature associated withcorrosion and/or adhesion can be extracted from a waveform in the timedomain.

Three different types of test blocks of reinforced concrete listed belowwere prepared and compared with each other.

-   -   (A) Normal reinforced concrete.    -   (B) Normal reinforced concrete was fatigued using a fatigue test        machine until a slight crack starting from a reinforcing iron        rod was produced.    -   (C) Normal reinforced concrete was fatigued using a fatigue test        machine beyond the state of the test sample (B) until adhesion        between a reinforcing iron rod and concrete was lost.

The test blocks were all produced using 13D reinforcing iron rods(deformed reinforcing iron rods with a diameter of 13 mm) so as to haveexternal dimensions of 200 mm×150 mm× and 100 mm and a cover depth d of30 mm.

A coil 12 and an acoustic transducer 14 were attached to a surface ofeach test block, and a current pulse with a crest value of 2000 A and apulse width of 350 μs was applied to each coil 12 thereby exciting thereinforcing iron rod.

FIGS. 10(a), 10(b), and 10(c) are diagrams showing waveforms in the timedomain output by the acoustic transducers attached to the respectivetest blocks (A), (B), and (C) and measured by the measurement unit.

As can be seen from those figures, for the normal reinforced concreteblock (A), a waveform having a triangle-like shape having a symmetryaxis and a vertex along the time axis was obtained.

On the other hand, for the test block (B) having a crack, a waveformhaving a rectangle-like shape having a symmetry axis and a vertex alongthe time axis was obtained.

However, for the test block (C) having substantially no adhesion betweenthe reinforcing iron rod and the concrete, substantially no outputwaveform was observed.

As described above, by displaying waveforms in the time domain measuredby the measurement unit of the apparatus according to the presentinvention, it is possible to detect differences in corrosion and/oradhesion of reinforcing iron rods from the waveforms.

Now, a fourth example is described below.

In this fourth example, it is demonstrated that a feature associatedwith corrosion and/or adhesion can be extracted from waveforms in thetime domain also in a case in which an acoustic transducer (AE sensor)is attached to an exposed part of a reinforcing iron rod of reinforcedconcrete as shown in FIG. 1(b).

Test blocks similar to those used in the third example were used, and anexperiment was performed in a similar manner to the example 3 except forthe attaching location of each acoustic transducer.

FIGS. 11(a), 11(b), and 11(c) are diagrams showing waveforms in the timedomain output by the acoustic transducers directly attached toreinforcing iron rods of the respective test blocks (A), (B), and (C)and measured by the measurement unit.

As can be seen from those figures, substantially no output waveform wasobserved for the normal reinforced concrete (A). This is because strongadhesion between the reinforcing iron rod and the concrete causes avibration produced by exciting the reinforcing iron rod to be quicklyattenuated.

On the other hand, for the test block (B) having a crack, a waveformhaving a triangle-like shape having a symmetry axis and a vertex alongthe time axis was obtained.

However, for the test block (C) having substantially no adhesion betweenthe reinforcing iron rod and the concrete, a waveform having atriangle-like shape having a symmetry axis and a vertex along the timeaxis was obtained, but the waveform has a long tail extending along thetime axis. This is because adhesion between the reinforcing iron rod andthe concrete was lost and a space was created between the reinforcingiron rod and the concrete, and thus a vibration of the reinforcing ironrod attenuates gradually. As a result, the vibration continues for along time.

As described above, by displaying waveforms in the time domain measuredby the measurement unit of the apparatus according to the presentinvention, it is possible to detect differences in corrosion and/oradhesion of reinforcing iron rods from the waveforms also in the case inwhich the acoustic transducer is attached directly to a reinforcing ironrod.

A process, performed by the measurement unit to extract a featureassociated with corrosion and/or adhesion from the shape factor or thecrest factor of the waveform in the time domain and display informationwhether or not there is a problem associated with corrosion and/oradhesion, is described below.

First, formulas used in the signal processing program performed by themeasurement unit to determine the shape factor and the crest factor aredescribed.

Let x_(i) denote each data value of a waveform in the time domain, andlet N denote the total number of data.

An average value x_(av) is defined by the following formula:$x_{av} = \frac{\sum\limits_{i = 1}^{N}\quad x_{i}}{N}$

An effective value x_(rms) is defined by the following formula:$x_{r\quad m\quad s} = \sqrt{\frac{\sum\limits_{i = 1}^{N}\quad x_{i}^{2}}{N}}$

A peak value x_(p) is defined by the following formula:$x_{p} = {\max\limits_{i \in N}\left\{ x_{i} \right\}}$

The shape factor SF is defined by the following formula:${SF} = \frac{x_{r\quad m\quad s}}{{\overset{\_}{x}}_{av}}$

The crest factor CF is defined by the following formula:${CF} = \frac{x_{p}}{x_{r\quad m\quad s}}$

A fifth example is described below.

In this fifth example, the shape factor SF and the crest factor CF weredetermined in accordance with above-described formulas (1) to (5) fromthe waveforms in the time domain measured in the example 3 for therespective test blocks (A), (B), and (C), and a comparison was made.

FIG. 12 is a table showing the shape factors SF and the crest factors CFfor the respective test blocks (A), (B), and (C).

As can be seen from FIG. 12, the shape factor SF and the crest factor CFsignificantly vary depending on the test blocks, that is, depending onthe adhesion of the reinforcing iron rod.

As described above, the measurement unit calculates the shape factor SFand the crest factor CF of a structure to be examined in accordance withthe signal processing program and compares the calculated shape factorSF and the crest factor CF with respect to threshold valuespredetermined as, for example, 1.50 for the shape factor and 5.50 forthe crest factor in FIG. 12. It is determined whether there is noproblem depending on whether the shape factor or the crest factor of thestructure under examination are greater than the corresponding thresholdvalue, and information indicating whether or not there is a problem isdisplayed.

A process, performed by the measurement unit to determine a similarityfactor by extracting a feature associated with corrosion and/or adhesionfrom the shape of the envelope curve of the waveform in the time domainand display information whether or not there is a problem associatedwith corrosion and/or adhesion, is described below.

First, formulas used in the signal processing program performed by themeasurement unit to determine the similarity factor are described.

First, the absolute value x_(i) is determined for each data value of thewaveform in the time domain. The absolute values are put one afteranother in the same order as that in which the waveform was sampled, andan envelope curve which smoothly envelopes the series of the absolutevalues is calculated. Let y_(i) denote each data value of the envelopecurve.

A probability P(y_(i)) is defined by the following formula:${P\left( y_{i} \right)} = \frac{y_{i}}{\sum\limits_{i = 1}^{N}\quad y_{i}}$

Let P_(a)(y_(i)) be the probability P(y_(i)) for the structure in aninitial state, and P_(b)(y_(i)) be probability P(y_(i)) for thestructure used for a particular period of time, then the amount ofinformation IF(y_(i)) can be defined by the following formula:${{IF}\left( y_{i} \right)} = {\log\frac{P_{a}\left( y_{i} \right)}{P_{b}\left( y_{i} \right)}}$

The similarity factor SF is defined by the following formula:${SF} = {\sum\limits_{i = 1}^{N}{\log\frac{P_{a}\left( y_{i} \right)}{p_{b}\left( y_{i} \right)}}}$

Now, a sixth example is described below.

In this sixth example, the envelope curves were determined from thewaveforms in the time domain, determined in the example 3 for therespective test blocks (A), (B), and (C), and a comparison in terms ofthe similarity factor was performed.

FIG. 13(a) shows the envelope curves determined for the respective testblocks (A), (B), and (C), and FIG. 13(b) shows the correspondinglogarithmic inverse envelope curves. Herein, the logarithmic inverseenvelope curve refers to an envelop curve for the logarithm value of theinverse of the probability P(y_(i)).

As can be seen from FIG. 13(a), the envelope curves of the test blocks(B) and (C) are significantly different from that of the test block (A).Thus, by comparing an envelope curve such as that for the test block (B)or (C) with respect to an envelope curve in an initial state such asthat for the test block (A), it is possible to detect an occurrence ofcorrosion and/or a reduction in adhesion.

As can be seen from FIG. 13(b), also in the logarithmic inverse envelopecurves, a clear difference relative to the initial state appears, andthus the similarity factor obtained by adding the differences along thetime axis is used to diagnose corrosion and/or adhesion.

As described above, in accordance with the signal processing program,the measurement unit calculates the envelope curve, the logarithmicinverse envelope curve, and the similarity factor and compares thesimilarity factor with the predetermined threshold value. Depending onwhether the similarity factor is greater than or equal to or smallerthan the threshold value, information indicating whether or not there isa problem is displayed.

The measurement unit may extract a feature associated with corrosionand/or adhesion from a normalized waveform obtained by dividing eachvalue of a waveform in the time domain by the effective value of thewaveform or from a waveform obtained by exponentiating the normalizedwaveform whereby information associated with the corrosion and/oradhesion may be displayed. This technique is described in further detailbelow.

The normalized waveform can be obtained by dividing the data value X_(i)of the waveform in the time domain by the effective value x_(rms) givenby formula (2).

With reference to a seventh example, the technique is described further.

In this seventh example, the normalized waveform and the exponentiationof the waveform thereof are calculated for the respective test blocks(A), (B), and (C) from the time-domain waveforms measured in the example3 for the respective test blocks (A), (B), and (C).

FIGS. 14(a), 14(b), and 14(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (A).

FIGS. 15(a) and 15(b) respectively show the cube and the quartic of thenormalized waveform of the test block (A).

FIGS. 16(a), 16(b), and 16(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (B).

FIGS. 17(a) and 17(b) respectively show the cube and the quartic of thenormalized waveform of the test block (B).

FIGS. 18(a), 18(b), and 18(c) respectively show the time-domainwaveform, the normalized waveform, and the square of the normalizedwaveform, obtained for the test block (C).

FIGS. 19(a) and 19(b) respectively show the cube and the quartic of thenormalized waveform of the test block (C).

As can be seen from FIGS. 14 to 19, the normalized waveform and theexponentiation of the waveform thereof indicate more clearly thedifference in the degree of corrosion and/or adhesion among the testblocks (A), (B), and (C) than can be indicated by the time-domainwaveform. In particular, the waveforms obtained by means of a high-orderexponentiation significantly differ depending on the degree of corrosionand/or adhesion.

As described above, by evaluating the normalized waveform or theexponentiation of the waveform thereof, it is possible to perform thehigh-sensitive detection of corrosion and/or adhesion.

As described above, in accordance with the signal processing program,the measurement unit extracts a feature by calculating the normalizedwaveform and the exponentiation of the waveform thereof from thetime-domain waveform, determines, on the basis of comparison withthreshold values, whether or not there is a problem associated withcorrosion and/or adhesion, and displays the result.

The measurement unit may extract a feature associated with corrosionand/or adhesion from a frequency-domain waveform and may displayinformation indicating whether or not there is a problem associated withcorrosion and/or adhesion, as described in detail below.

The frequency-domain waveform is determined by the measurement unit byperforming a Fourier transform on a time-domain waveform in accordancewith the signal processing program.

With reference to an eighth example, the technique is described infurther detail below.

In this eighth example, the frequency-domain waveform is determined byperforming a Fourier transform on each of the time-domain waveformsdetermined in the third or fourth example for the test blocks (A), (B),and (C), and the resultant frequency-domain waveforms of the test blocks(A), (B), and (C) are compared with each other.

FIGS. 20(a), 20(b), and 20(c) respectively show frequency-domainwaveforms of the test blocks (A), (B), and (C), determined from thetime-domain waveforms determined in the third example for the testblocks (A), (B), and (C).

As can be seen from FIG. 20(a), in the case of the test block (A) ofnormal reinforced concrete, the frequency spectrum includes componentsdistributed randomly and substantially continuously in a frequency rangeof 20 kHz to 80 kHz.

On the other hand, as can be seen from FIG. 20(b), in the case of thetest block (B) of reinforced concrete having a crack, particularfrequency components appear at particular intervals.

In the case of the test block (C) in which adhesion of a reinforcingiron rod was lost, as can be seen from FIG. 20(c), particular frequencycomponents appear at particular intervals, although the tendency is notstrong compared with the text block (B). Another feature of this testblock (C) is that the frequency-domain waveform includes a largecomponent near 150 kHz.

The difference between FIGS. 20(a) and 20(b), that is, between the textblock (A) and the test block (B) is very great. This makes it possibleto easily detect the difference even in the case in which the differencecannot be easily detected from the time-domain waveforms.

FIGS. 21(a), 21(b), and 21(c) respectively show frequency-domainwaveforms of the test blocks (A), (B), and (C), determined from thetime-domain waveforms determined in the fourth example for the testblocks (A), (B), and (C) by using the acoustic transducers attacheddirectly to reinforcing iron rods.

As can be seen from those figures, in the case in which the acoustictransducers are directly attached to reinforcing iron rods, particularfrequency components appear at particular intervals with decreasingadhesion, as in the case shown in FIG. 20.

As described above, in accordance with the signal processing program,the measurement unit calculates the frequency-domain waveform from atime-domain waveform and compares the resultant frequency-domainwaveform with a reference pattern thereby determining the similarity.The similarity is then compared with a threshold value of similarity.Depending on whether the similarity is equal to or smaller than thethreshold value, it is determined whether or not there is a problem, andinformation indicating the result is displayed.

The measurement unit may determine the normalized waveform or theexponentiation of the normalized waveform from a frequency-domainwaveform in a similar manner as described above with reference to thesixth or seventh example, and may perform a high-sensitive extraction ofa feature associated with corrosion and/or adhesion using the normalizedwaveform or the exponentiation of the normalized waveform. Furthermore,the similarity factor may be calculated from the normalized waveform orthe exponentiation of the normalized waveform, and the resultantsimilarity factor may be compared with a predetermined threshold valuethereby performing a high-sensitive detection of whether the similarityfactor of a structure under examination is equal to or smaller than thethreshold value. In accordance with the result, information indicatingwhether or not there is a problem is displayed.

A method of measuring the cover depth of reinforced concrete or thediameter of a reinforcing iron rod according to the present invention isdescribed below.

FIG. 22(a) is a diagram showing a method of measuring the diameter orthe cover depth of a reinforcing iron rod according to the presentinvention, and FIG. 22(b) is a graph showing a measurement result.

As described in FIG. 22(a), a coil 12 is attached to a surface ofreinforced concrete 11, at a location exactly above a reinforcing ironrod 11 a, and an acoustic transducer 14 is attached to the surface ofthe reinforced concrete 11. The reinforcing iron rod 11 a is thenexcited by a magnetic field pulse generated by the coil 12, therebygenerating an acoustic signal from the reinforcing iron rod 11 a. Theacoustic signal is converted into an electric signal by the acoustictransducer 14 and supplied to a measurement unit 15. The measurementunit 15 extracts a feature value such as the peak-to-peak value of thecrest value of the acoustic signal. If the cover depth d is known, thediameter of the reinforcing iron rod can be determined from theextracted feature value and the cover depth d on the basis of thepredetermined correspondence among the feature value, the diameter ofreinforcing iron rod, and the cover depth. In a case in which the coverdepth d is unknown, the cover depth d can be determined in accordancewith the technique disclosed in claim 2 of the present invention.

In a case in which the diameter of the reinforcing iron rod is known butthe cover depth d is unknown, the cover depth d is determined from thedetected feature value and the diameter of the reinforcing iron rod onthe basis of the predetermined correspondence among the feature value,the diameter of the reinforcing iron rod, and the cover depth.

In FIG. 22(b), the vertical axis represents the feature value. In thisspecific example, the peak-to-peak value of the crest value is employedas the feature value. The horizontal axis represents the cover depth d.As shown in an insertion in FIG. 22(b), the dependence of the featurevalue on the cover depth d was determined for various diameters of thereinforcing iron rods 10 d, 13 d, 16 d, 19 d, and 25 d (deformedreinforcing iron rods with diameters of 10 mm, 13 mm, 16 mm, 19 mm, and25 mm).

As can be seen from FIG. 22(b), the feature value depends on both thediameter of the reinforcing iron rod and the cover depth d. Thus, on thebasis of the dependence determined above, it is possible to determinethe cover depth d or the diameter of the reinforcing iron rod.

A method of diagnosing/measuring whether a binding member is securelyfastened according to claim 19 of the present invention is describedbelow.

FIGS. 23(a) and 23(b) are diagrams showing a method of diagnosing ormeasuring the secureness of a binding member, according to the presentinvention, wherein FIG. 23(a) is a side view of a conductor 21 and aconductor 22 bound together via a bolt 23 and a nut 24, and FIG. 23(b)is a plan view thereof.

A coil 12 is disposed exactly above the bolt 22 binding the conductor21, and acoustic transducers 14R and 14L are attached to the surfaces ofthe respective conductors 21 and 22. If a magnetic filed pulse isgenerated by the coil 12, an eddy current is induced in the surface ofthe conductor 21 and a magnetic field generated by the eddy currentinteracts with the magnetic field of the magnetic field pulse wherebythe conductor 21 is oscillated. If the bolt 23 and the nut 24 arescrewed in a securely fastened state, an acoustic signal generated inthe conductor 21 propagates to the conductor 22 without having asignificant attenuation and thus acoustic signals detected by theacoustic transducer 14R and the acoustic transducer 14L become nearlyequal in magnitude. However, if the bolt 23 and the nut 24 are screwedin a loose state, an acoustic signal generated in the conductor 21 doesnot propagate easily into the conductor 22, and thus a difference occursbetween acoustic signals detected by the acoustic transducer 14R and theacoustic transducer 14L.

Thus, it is possible to evaluate whether binding members are in asecurely fastened state.

A ninth example is described below.

In this ninth example 9, it is demonstrated that the fastening state ofbinding members can be evaluated using the method ofdiagnosing/measuring a fastening state of a binding member according tothe present invention.

Two aluminum plates (200×300×3t) were bound with six sets of stainlesssteel bolts ad nuts (M10×15). A current pulse with a crest value of 2000A and a pulse width of 350 μs was applied to the coil.

FIGS. 24(a) to 24(d) shows a measurement result obtained when the boltsand nuts were in a securely fastened state, wherein FIGS. 24(a) and24(b) show output waveforms of the acoustic transducer 14R attached tothe conductor 21 facing the coil, and FIGS. 24(c) and 24(d) show outputwaveforms of the acoustic transducer 14L attached to the conductor 22bound with the conductor 21 using the bolts and nuts.

Note that FIGS. 24(a) and 24(c) show waveforms obtained by passing theoriginal output waveforms of the acoustic transducer through a bandpass(BP) filter (having a passband of 20 kHz to 500 kHz) thereby removingfrequency components lower than 20 kHz, while FIGS. 24(b) and 24(d) showwaveforms including whole frequency components up to 500 kHz.

As can be seen from those figures, when the bolt and the nut aresecurely fastened, the output waveform of the acoustic transducer 14L issubstantially equal to that of the acoustic transducer 14R.

FIGS. 25(a) to 25(d) are diagrams showing a measurement result obtainedwhen the bolt and the nut are in a loosely coupled state, wherein FIGS.25(a) and 25(b) show output waveforms of the acoustic transducer 14Rattached to the conductor 21 located closer to a coil, and FIGS. 25(c)and 25(d) show output waveforms of the acoustic transducer 14L attachedto the conductor 22 bound with the conductor 21 by the bolt and the nut.Note that FIGS. 25(a) and 25(c) show waveforms obtained by passing theoriginal output waveforms of the acoustic transducer through a bandpass(BP) filter (having a passband of 20 kHz to 500 kHz) thereby removingfrequency components lower than 20 kHz, while FIGS. 25(b) and 25(d) showwaveforms including whole frequency components up to 500 kHz.

As can be seen from those figures, when the bolt and the nut are notsecurely fastened, the output waveform of the acoustic transducer 14L issmaller in amplitude than that of the acoustic transducer 14R.

As described above, this method of the present invention makes itpossible to diagnose or measure whether a binding member is securelyfastened.

This method can also be used to detect a crack in a honeycomb structureused in a bridge or the like. Furthermore, the method can also be usedto determine whether connection is well welded.

A method of measuring the location of a conductor embedded in anon-conductive material according to the present invention is describedbelow.

FIGS. 26(a) and 26(b) are diagrams showing a method of measuring thelocation of a conductor embedded in a non-conductive material, whereinFIG. 26(a) is a side view showing a manner in which an acoustictransducer 14 is attached to an exposed part 33 of a water pipe 32buried in the ground 31 which is non-conductive, and a coil 12 isdisposed on the surface 34 of ground 31, and FIG. 26(b) is a plan viewthereof.

If a magnetic field pulse is generated by the coil 12, an eddy currentis induced in the surface of the water pipe 32, and the water pipe 32 isoscillated as a result of interaction between the magnetic fieldassociated with the eddy current and the magnetic field of the magneticfield pulse. An acoustic wave generated by the oscillation of the waterpipe 32 propagates to the exposed part 33 of the water pipe 32 and isdetected by the acoustic transducer 14. The strength of the acousticsignal becomes highest when the coil 12 is put at a location exactlyabove the water pipe 32. By changing the location of the coil 12 andlooking for a location at which the strength of the acoustic signalbecomes highest, the location of the water pipe 32 can be detected.

Now, a tenth example is described.

In this tenth example, it is demonstrated that the location of aconductor embedded in a non-conductive material can be detected by theabove-described method according to the present invention.

FIGS. 27(a) to 27(c) are graphs showing results of measurement of thelocation of a water pipe buried in the ground, wherein FIG. 27(a) showsthe waveform of an acoustic signal detected by the coil disposed exactlyabove the water pipe, FIG. 27(b) shows a waveform detected by the coillocated 60 mm apart from the location exactly above the water pipe, FIG.27(c) shows a waveform detected by the coil located 180 mm apart fromthe location exactly above the water pipe.

As can be seen from those figures, the strength of the acoustic signalbecomes highest when the coil is located exactly above the water pipe,the strength of the acoustic signal decreases with the distance betweenthe coil and the position exactly above the water pipe. Thus, if thelocation of the coil is changed and the location at which the acousticsignal becomes highest is determined, the location of the water pipemust be exactly below the location at which the acoustic signal becomeshighest.

A method of determining whether a conductor embedded in a non-conductivematerial has a fracture and/or determining the location of such afracture according to the present invention is described below.

FIG. 28 is a diagram showing a method of diagnosing whether a conductorembedded in a non-conductive material has a fracture and a method ofmeasuring the location of the fracture.

An acoustic transducer 14 is attached to an exposed part 43 of areinforcing iron rod 42 embedded in reinforced concrete 41 with anelongated shape. A coil 12 is attached to a surface of the elongatedreinforced concrete 41. An eddy current is induced in the surface of areinforcing iron rod by generating a magnetic field pulse from the coil12. As a result, the reinforcing iron rod 42 is excited by theinteraction between the magnetic field associated with the eddy currentand the magnetic field of the magnetic field pulse. An acoustic wave isgenerated by the excited reinforcing iron rod 42 and propagates throughthe reinforcing iron rod 42. The acoustic wave propagating through thereinforcing iron rod 42 is detected by the acoustic transducer 14attached to the exposed part 43 of the reinforcing iron rod 42. If thereinforcing iron rod 42 has a fracture at some location 44, the strengthof the detected acoustic signal is small, and thus the reinforcing ironrod 42 can be regarded as having a fracture. By changing the location ofthe coil 12 across the surface of the elongated reinforced concrete 41and detecting a position at which the acoustic signal abruptly becomesstrong, the location 44 of the fracture can be determined.

As described above, the present invention makes it possible to determinewhether a reinforcing iron rod has a fracture and further determine thelocation of such a fracture.

Although the present invention has been described above with referenceto specific embodiments, the invention is not limited to thoseembodiments but various modifications, additions, and eliminations arepossible without departing from the spirit and the scope of theinvention. It should be understood that the scope is defined by theclaims appended hereto.

Industrial Applicability

According to the present invention, as described above, a conductor in astructure including the conductor and a non-conductive material coveringthe conductor can be directly and strongly excited by a pulse ofelectromagnetic force. Thus, for example, when a reinforcing iron rod inreinforced concrete is excited, a very large acoustic signal, which isinfluenced by corrosion and/or adhesion of the reinforcing iron rod, isobtained. This makes it possible to non-destructively and preciselydiagnose/measure the location, corrosion, adhesion strength, and/or rustof the reinforcing iron rod and further a separation or a crack of theconcrete, regardless of the thickness of the concrete and regardless ofthe degree of degradation.

Therefore, it becomes possible to diagnose/measure, very easily in ahighly reliable fashion, a structure made of reinforced concrete such asa tunnel, a bridge, a building, retaining wall, dam, and civilengineering construction, thereby making it possible to performmaintenance/management of the structure made of reinforced concrete in ahighly reliable fashion.

Furthermore, according to the method of acoustic diagnosis/measurementusing a pulse of electromagnetic force of the present invention, it ispossible to measure the cover depth of a reinforcing iron rod and/or thediameter of reinforcing iron rod. Furthermore it is also possible todetermine whether a binding member such as a set of a bolt and a nut issecurely fastened. The location of a water pipe or a gas pipe buried inthe ground can also be detected. It is also possible to determinewhether a reinforcing iron rod has a fracture. Suchdiagnosis/measurement can be performed easily and in a highly reliablefashion.

1. An acoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force, comprising a coil attached to a surface of astructure including a conductor and a non-conductive material coveringthe conductor; a power supply unit for supplying a current pulse to thecoil; an acoustic transducer attached to the surface of the structure orto a part of the conductor, the part being separated from thenon-conductive material; and a measurement unit for measuring an outputwaveform of the acoustic transducer, wherein corrosion of the conductorand/or adhesion strength of the conductor are diagnosed or measured,wherein the non-conductive material is concrete.
 2. An acousticdiagnosis/measurement apparatus using a pulse of electromagnetic force,comprising: a coil attached to a surface of a structure including aconductor and a non-conductive material covering the conductor; a powersupply unit for supplying a current pulse to the coil; and adisplacement detector for optically measuring displacement of thesurface of the structure thereby measuring a vibration of the surface ofthe structure, wherein corrosion of the conductor, and/or adhesionstrength of the conductor are diagnosed or measured, wherein thenon-conductive material is concrete.
 3. An acousticdiagnosis/measurement apparatus using a pulse of electromagnetic force,according to claim 1 or 2, wherein the acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force includes a plurality ofsubcoils, the plurality of subcoils being disposed coaxially such thatadjacent subcoils are in close contact with each other; and the powersupply unit includes charge storage capacitors connected in series tothe respective coils and a power source connected, via a common switchand in parallel, to each series connection of one coil and one capacitorwhereby a current pulse is applied to coils by turning on the switchthereby generating a magnetic field pulse.
 4. An acousticdiagnosis/measurement apparatus using a pulse of electromagnetic force,according to claim 1 or 2, wherein a magnet for generating a staticmagnetic field is added to the coil.
 5. An acousticdiagnosis/measurement apparatus using a pulse of electromagnetic force,according to claim 1 or 2, wherein the acoustic transducer is an elementfor converting an acoustic signal into an electric signal, selected froma group consisting of an acoustic emission sensor, an accelerationsensor, and a microphone.
 6. An acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force according to claim 1, wherein themeasurement unit for measuring the output waveform measures the outputwaveform in the time domain, displays the measured output waveform,extracts a feature associated with corrosion and/or adhesion from thewaveform in the time domain, and displays the extracted feature.
 7. Anacoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force according to claim 6, wherein the featureextracted from the waveform in the time domain is a pattern, a shapefactor, or a crest factor of the waveform in the time domain; and thedisplaying of information associated with the corrosion and/or adhesionincludes comparing the form factor or the crest factor with apredetermined threshold value and displaying whether or not there is aproblem in terms of the corrosion and/or the adhesion.
 8. An acousticdiagnosis/measurement apparatus using a pulse of electromagnetic forceaccording to claim 6, wherein the feature extracted from the waveform inthe frequency domain is a waveform pattern in the frequency domain; andthe displaying of information associated with the corrosion and/oradhesion includes comparing the waveform pattern with a predeterminedpattern, and displaying whether or not there is a problem in terms ofthe corrosion and/or the adhesion.
 9. An acoustic diagnosis/measurementapparatus using a pulse of electromagnetic force according to claim 6,wherein the feature extracted from the waveform in the frequency domainis a normalized waveform obtained by dividing each value of the waveformin the frequency domain by the effective value of the waveform in thefrequency domain or a waveform obtained by exponentiating the normalizedwaveform; and the displaying of information associated with thecorrosion and/or adhesion includes extracting the similarity factor fromthe envelope curve of the normalized waveform, comparing the similarityfactor with a predetermined threshold value, and displaying whether ornot there is a problem in terms of the corrosion and/or the adhesion.10. An acoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force according to claim 2, wherein the displacementdetector is a laser interferometer for illuminating a surface of thestructure with a coherent laser beam and detecting a phase difference asan interference pattern of a reflected laser beam, the phase differencevarying depending on a vibration of a surface of the structure.
 11. Anacoustic diagnosis/measurement apparatus using a pulse ofelectromagnetic force, comprising a coil attached to a surface of astructure including a conductor and a non-conductive material coveringthe conductor; a power supply unit for supplying a current pulse to thecoil; and acoustic transducer attached to the surface of the structureor to a part of the conductor, the part being separated from thenon-conductive material; and a measurement unit of measuring an outputwaveform of the acoustic transducer in the time domain, displays themeasured output waveform in the time domain, extracts a featureassociated with corrosion and/or adhesion from the waveform in the timedomain, and displays the extracted feature, wherein the extractedfeature is a similarity factor extracted from the shape of the envelopecurve of the waveform in the time domain and the displaying ofinformation associated with the corrosion and/or adhesion includescomparing the similarity factor with a predetermined threshold value anddisplaying whether or not there is a problem in terms of the corrosionand/or the adhesion.
 12. An acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force, comprising a coil attached to asurface of structure including a conductor and a non-conductive materialcovering the conductor; a power supply unit for supplying a currentpulse to the coil; an acoustic transducer attached to the surface of thestructure or to a part of the conductor, the part being separated fromthe non-conductive material; and a measurement unit for measuring anoutput waveform of the acoustic transducer in the time domain, whereinthe measurement unit measures the output waveform in the time domain,displays the measured output waveform in the time domain, extracts afeature associated with corrosion and/or adhesion from the waveform inthe time domain, and displays the extracted feature, wherein theextracted feature is a waveform obtained by the exponentiation of anormalized waveform which is obtained by dividing each value of thewaveform in the time domain by the effective value of the waveform inthe time domain.
 13. An acoustic diagnosis/measurement apparatus using apulse of electromagnetic force according to claim 12, wherein asimilarity factor is extracted from the envelope curve of the normalizedwaveform and compared with a predetermined threshold value, andinformation indicating whether or not there is a problem in terms of thecorrosion and/or the adhesion is displayed.
 14. A method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of: attaching a coil to a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; convertingan acoustic signal of the acoustic wave into an electric signal by usingan acoustic transducer attached to the surface of the structure orattached to a part of the conductor, the part of the conductor beingseparated from the non-conductive material; and measuring the waveformof the electric signal to perform diagnosis and/or measurement in termsof corrosion and/or adhesion of the conductor, wherein thenon-conductive material is concrete.
 15. A method of acousticdiagnosis/measurement using a pulse of electromagnetic force, comprisingthe steps of: attaching a coil to a surface of a structure including aconductor and a non-conductive material covering the conductor; applyinga current pulse to the coil thereby generating a magnetic field pulse;inducing an eddy current in the conductor by the magnetic field pulse;oscillating the conductor by interaction between the eddy current andthe magnetic field pulse thereby generating an acoustic wave; detectingan optical displacement corresponding to a surface vibration of thestructure generated by the acoustic wave thereby diagnosing the locationof the conductor and the state of the structure, wherein thenon-conductive material is concrete.
 16. An acousticdiagnosis/measurement apparatus using a pulse of electromagnetic force,comprising a coil attached to a surface of a structure including aconductor made of magnetic material and a non-conductive materialcovering the conductor; a power supply unit for supplying a currentpulse to the coil; an acoustic transducer attached to the surface of thestructure or to a part of the conductor, the part being separated fromthe non-conductive material; and a measurement unit for measuring anoutput waveform of the acoustic transducer, wherein the conductor madeof magnetic material is further oscillated than a conductor made ofnon-magnetic material by a force associated with magnetic energy of theconductor made of magnetic material, and corrosion of the conductor madeof magnetic material and/or adhesion strength of the conductor made ofmagnetic material are diagnosed or measured, wherein the non-conducivematerial is concrete.
 17. An acoustic diagnosis/measurement apparatususing a pulse of electromagnetic force, comprising: a coil attached to asurface of a structure including a conductor made of magnetic materialand a non conductive material covering the conductor; a power supplyunit for supplying a current pulse to the coil; and a displacementdetector for optically measuring displacement of the surface of thestructure thereby measuring a vibration of the surface of the structure,wherein the conductor made of magnetic material is further oscillatethan a conductor made of non-magnetic material by a force associatedwith magnetic energy of the conductor made of magnetic material, andcorrosion and/or adhesion strength of the conductor made of magneticmaterial are diagnosed or measured wherein the non-conductive materialis concrete.
 18. An acoustic diagnosis/measurement apparatus using apulse of electromagnetic force, according to claim 16 or 17, wherein theconductor made of magnetic material is an iron rod and thenon-conductive material covering the conductor is concrete.
 19. A methodof acoustic diagnosis/measurement using a pulse of electromagneticforce, comprising the steps of: attaching a coil to a surface of astructure including a conductor made of magnetic material and anon-conductive material covering the conductor; applying a current pulseto the coil thereby generating a magnetic field pulse; inducing an eddycurrent in the conductor made of magnetic material by the magnetic fieldpulse; oscillating the conductor made of magnetic material byinteraction between the eddy current and the magnetic field pulsethereby generating an acoustic wave, wherein the conductor made ofmagnetic material is further oscillated than a conductor made ofnon-magnetic material by a force associated with magnetic energy of theconductor made of magnetic material; converting an acoustic signal ofthe acoustic wave into an electric signal by using an acoustictransducer attached to the surface of the structure or attached to apart of the conductor made of magnetic material, the part of theconductor made of magnetic material being separated from the structure;and measuring the waveform of the electric signal to perform diagnosisand/or measurement in terms of corrosion and/or adhesion of theconductor made of magnetic material, wherein the non-conductive materialis concrete.
 20. A method of acoustic diagnosis/measurement using apulse electromagnetic force, according to claim 19, wherein theconductor made of magnetic material is an iron rod and thenon-conductive material covering the conductor is concrete.